In a conventional art, a hand back support plate tied by a hand using a band at an intermediate plate, which is connected at a front end of a wrist mounted plate rotatably in left and right directions, is connected rotatably in a vertical direction, with the wrist mounted plate being mounted at a wrist using a band. A horizontal angle adjusting member is provided for adjusting a horizontal angle of the intermediate plate with respect to a wrist mounted plate, and a vertical angle adjusting member is provided for adjusting a vertical angle of the hand back support plate. The horizontal and vertical angle adjusting members are mounted on an upper surface of the intermediate plate. A bowling player wears the above device at a wrist and plays a bawling game while adjusting the horizontal and vertical angles of the hand back support plate while the player releases first and second times. However, in the conventional art, so as to adjust the horizontal angle of the hand back support plate, it is needed operate the horizontal angle adjusting member with the other hand which does not wear the above device, and the horizontal angle of the hand back support plate is adjusted as the intermediate plate is rotated, and then the vertical angle adjusting member is operated for thereby adjusting the vertical angle of the hand back support plate. In the conventional art, the angle adjusting work is too complicated, and the horizontal and vertical angle adjusting members are separately provided. So, the construction of the entire system is so complicated, and the volume is too large. The manufacture cost increases, and the product is expensive and too heavy.